Electric-light signal



March 24, 1 931. Q; mM 1,797,880

- Y I ELECTRIC LIGHT SIGNAL Filed March 10, 1927 Patented Mu. 24, 1931 UNITED STATES'PATENT. OFFICE OTTO BCHIRM, OI BERLIN-KALENSEE, GERMANYyASSIGNORTO SIEMENS 6t HALSKE,

AKTIENGESELLSCHAFT, OF SIEMENSSTADT, NEAR BERLIN, GERMANY, A CORPORA- TION OF GERMANY ELECTRIC-LIGHT SIGNAL Application filed March 10, 1927, Serial No. 174,352, and in Germany March 30,1926.

My invention relates to electric light signals, and more particularly to light signals in which a plurality of lamps are lighted up.

alternately. Such si nal systems have the disadvantage, that t e incandescent bulbs are very quickly worn out owing to the lamps being frequently switched on and off.

This is due to the fact that the metal filament lamp has a lower resistance when it is 10 switched on i. e. is still in the cold state, than after it has been heated by the passage of the current. They thus permit a larger current to pass when just switched in than after they have been heated. Since at normal operation of these lamps the filaments are already loaded nearly with the permissible maximum amount of current, in order to obtain greater light output, this current surge exceeding the strength of this safe working current and taking place on closing the lamp circuit brings about a change in the structure of the metal wire which very quickly leads to the burning out of the lamp. This drawback becomes particularly noticeable in incandescent lamps which are frequently switched on and oil", as for instance in illuminated advertising signs, intermittent signal lights, signal plants and the like and is particularly striking in signals oper- 30 ated with high intensity lamps, as for instance railroad signals and above all trailic signals. In signals in which a particularly high light intensity is demanded and which consequently must be operated normally near the highest permissible current intensities there is the further drawback that sparking occurs at the contacts of the switches when the circuit is opened which leads to quick wear of the switches. This is, for instance, the case in day light signals of railroad safety systems and above all in street traific regulation signals in which the lamps are switched on and oil at intervals of a few seconds or minutes.

According to my invention this drawback is eliminated by connecting two or more of the alternately lighted lamps in series and placing a switch in shunt to simultaneously ighted lamps. With this system or arrangement it is possible to remove the short circuit of a lamp or group of lamps before the other lamp or group of lamps are shortcircuited. For a short time all the lamps are supplied with current simultaneously and in this way it is prevented that any lamp switched in receives the full voltage at once.

In the drawing aiiixed hereto an embodiment of my invention is illustrated by a diagram of connections.

. Referring to this drawing, 1 and 2 are two lamps of a trailic regulating signal system which show, for instance, a red and a green light and should be lighted up alternately. In the state shown the current flows from the source of current or mains 3 across the line l, lamp 1, short-circuit line 5, the closed contact (5, line 8 back to the supply. Simultaneously a portion of the current coming from lamp 1 flows across lamp 2 and line b back to the supply. This partial current is, however, unable to light up the lamp 2. If it is now desired that the lamp 2 should be lighted up contact (3 is first broken and then contact 7 closed, so that lamp 2 first receives current across lamp 1 only and only afterwards across the short-circuit line 9.

A further improvement may be attained by not switching the lighted lamps oil altogether, but continuing to supply them with a smaller current. The current is then not able to light up the lamp, but prevents the filament wire from cooling down entirely. For this purpose a resistance is placed in the connecting line of the lamp terminals besides the switch.

According to my invention the result is attained that'on the one hand the lamps are not switched oil altogether and thus cannot cool down completely and on the other hand that the lamps do not receive the full voltage immediately they are switched on, but only after the temperature of the filament has been raised to the point at which no undue current rush can occur. Crystallization and other changes in the structure of the wire filament are thus effectively prevented and the life of the lamps is extended considerably. At the same time the advantage results that by switching the lamps on or off only a part of the current is switched on or off by making or breaking the contacts 6 and 7, so that sparking is greatly reduced at the contacts. The elimination of the drawbacks specified thus also permits the safe use of the lamps at greater current strengths and light intensities than heretofore.

Various modifications and changes may be I made'without departing from the spirit and z the scope of the invention, and I desire, there- I fore, that only such limitations shall be placed thereon as are imposed by the prior art.

I claim as my invention:

In an electric system for giving alternately different signals, in combination, at least tWO series connected metal filament lamps, each representing a diilerent signal, a source of current connected in series with said lamps, a

circuit in parallel to each vof said lamps, a switch in each of said parallel circuits, and

a resistance connected in series with said switch in each of the said parallel circuits and suitably dimensioned topermit suflicient cur- 3 rent to pass through the lamp whose shunt circuit is closed to maintain the filament heated but not lighted.

In testimony whereof I afiix m si ature.

. OTTO S H l Rll/L 

